The present invention is directed to a data processing system which includes a central or master controlled processor and a number of remote processors and, more particularly, it relates to a method and apparatus for polling both active and inactive remote processors as part of the data processing system.
With the cost of microprocessor chips dropping, their use in relatively low-cost data processing systems are increasing. In modern data terminal devices, microprocessors are incorporated in keyboards, displays, printers, etc. These devices are associated with the functional operation of the terminal device. Terminals are used in some business environments which require that certain of the operating devices such as a printer, keyboard and display may be added to the terminal or removed from the terminal at various times during the day in accordance with business conditions. Prior polling systems such as taught by U.S. Pat. No. 3,766,530, U.S. Pat. No. 3,866,175 and U.S. Pat. No. 4,071,908 set up groups of active remote devices which are then polled by the master processor. But if other remote devices are added to the communication network or removed, the polling system is unable to pick up the change in the polling sequence. It is therefore a principal object of this invention to provide a polling sequence which detects the removal or the addition of a remote processing device from the communication network. It is a further object of this invention to provide a high-speed polling sequence of both active and inactive remote processing devices associated with a communication network.